1. Field of the Invention
The invention relates to an apparatus for microscopic examination of biological specimens with precise control of the temperature of the specimen.
2. Prior Art
In the biological sciences, it has been a longstanding problem to maintain satisfactory control of the temperature at which a biological specimen is examined under a microscope.
The biological specimen is usually grown in a standard laboratory culture dish manufactured from a plastic. The biological specimen may be observed by microscope in the culture dish provided the microscope is set for low magnification and the viewing period is short. For longer viewing periods, however, it is necessary to maintain the specimen at a constant, controlled temperature. For higher magnification, it is necessary that the specimen be mounted on a surface of high optical transmissivity which is sufficiently thin to permit the use of high numeric aperture objective lenses.
Microscopic examination of the biological specimen at high magnification (400.times. or greater, for example) with a constant, controlled temperature has presented problems not resolved until the present invention.
If the specimen is to be viewed in the culture dish in which it was grown but at high magnification, then the standard plastic laboratory culture dish is not acceptable because the thickness of the plastic prevents the use of high numeric aperture objective lenses. Furthermore, where the microscopic viewing technique requires polarization of light, then a plastic culture dish is not acceptable as plastic will depolarize light.
In addition, plastic does not conduct heat well, resulting in long thermal time ratios which prevent the precise control of temperature necessary.
If the specimen is first removed from the culture dish and placed into some other apparatus appropriate for use with high numeric aperture objective lenses, then the biological specimen may be damaged. Furthermore, removal of the specimen from the culture dish in which it was grown to a viewing apparatus is time consuming. Even when the specimen is removed from the culture dish and placed into some other apparatus, there still remains the problem of placing the apparatus onto a heating device with sufficient control of heat transfer and measurement of temperature to assure precise temperature control.
There have been prior systems which enable the scientist to view the biological specimen with temperature control on the surface on which the specimen was grown. Such systems generally require that the culture dish itself be placed onto a stage which is electrically heated. The heat from the stage then transfers by conduction to the culture dish and then to the specimen. Such systems, while operable, generally feature imprecise temperature control with slow temperature stabilization. When perfusion liquids are added to the sample, temperature drops occur from which these systems are slow to recover.
These problems are solved by the present invention.